Problem 122 - A Complete Resource Book in Chemistry for JEE Main

Question

When the sample of copper with zinc impurity is to be purified by electrolysis, the appropriate electrodes are [2002] Cathode Anode \(\begin{array}{ll}\text { (a) pure zinc } & \text { pure copper }\end{array}\) (b) pure copper impure sample (c) impure zinc impure sample (d) impure sample pure copper

Step-by-Step Solution

Answer

The correct setup is option (b): pure copper as the cathode and impure sample as the anode.

Step 1: Understand Electrolysis Setup

Electrolysis is a process that uses electrical energy to bring about a chemical change. When purifying a metal, such as copper, via electrolysis, the impure metal is made the anode. Under the influence of an electric current, metal ions are transferred from the anode to the cathode.

Step 2: Identify the Cathode

The cathode is where the purified metal will deposit. In the electrolysis of copper, the cathode must be made of pure copper to attract copper ions from the solution, where they will deposit as copper metal.

Step 3: Identify the Anode

The anode is the source of metal ions. In this situation, the anode should be the impure sample containing copper, which is being purified, so that copper ions move from the anode to the cathode under the influence of the electric current.

Step 4: Determine the Correct Pairing

Considering the descriptions above: - The correct cathode for purification is pure copper. - The correct anode is the impure sample that contains copper to be refined. Thus, the configuration should have the cathode as pure copper and the anode as the impure copper sample.

Key Concepts

Copper Purification

Copper purification is an important process in metallurgy that ensures high-quality copper is obtained from its impure sources. This is often accomplished through a method called electrolysis. During electrolysis, electrical energy prompts a chemical change that separates the desired metal from impurities.

• Impure copper acts as the anode, the positive electrode.
• Pure copper, free of impurities, is deposited at the cathode, the negative electrode.

Copper purification involves dissolving the impure copper in an electrolyte solution. Once electricity is applied, copper ions move toward the cathode where they gain electrons and form pure copper metal. This leads to the removal of impurities, as they do not dissolve and often form residues at the bottom of the container. This ensures that the resulting metal is of high purity, suitable for industrial applications.

Anode and Cathode Identification

In the electrolysis process, identifying the correct electrodes is crucial. The anode and cathode serve distinct roles and are selected based on their composition and function in the electrolytic cell.

• Anode: The anode is typically the impure metal that needs purification. In copper electrolysis, the impure copper sample is made the anode. It is where oxidation occurs, meaning it loses electrons and releases metal ions into the electrolyte.
• Cathode: The cathode, in contrast, is made from pure metal, often pure copper when purifying copper. This electrode attracts metal ions from the solution, where they gain electrons and deposit as solid metal. This process is called reduction.

The correct identification and arrangement of these electrodes ensure the efficient transfer of ions, leading to successful purification.

Metal Refining Process

The metal refining process is a broad term that encompasses methods used to purify and improve the quality of metals. Electrolysis is one such method, particularly effective for metals like copper. This technique not only purifies metal but also refines its structure and properties.
Several key elements are involved in metal refining using electrolysis:

• Electrolyte: A solution that conducts electricity by moving ions, often containing the metal in an ionic form.
• Electrodes: As previously mentioned, the anode and cathode are essential. The anode is usually the impure metal, while the cathode is pure metal.
• Electricity: Provides the energy required to drive the ion exchange, crucial for the separation and deposition of pure metal at the cathode.

Metal refining ensures higher purity and can enhance the material's mechanical and electrical properties, making it indispensable in technology and industry.